Methane Coupling to Ethylene and Longer-Chain Hydrocarbons by Low-Energy Electrical Discharge in Microstructured Reactors

The direct conversion of methane to longer hydrocarbons, including alkanes and alkenes (i.e., olefins), is achieved with a high energy and atom efficiency through the use of low-energy, nonthermal electric glow discharge plasmas acting on CH4/O2/N2 and CH4/CO2/N2 in a microstructured reactor. The process is neither dependent on limited lifetime catalysts nor consumable chemicals, enabling continuous operation over long periods. Similarly, it is carried out at atmospheric pressure and ambient temperature, thus simplifying process implementation. Because it does not require high temperatures, energy is not wasted producing sensible heat, allowing for high process energy efficiencies. Also, because it is designed in easy to number up modules, it can be readily scaled to the needs of the methane resource available. The effects of CH4/O2 and CH4/CO2 ratios, electric discharge current, flow rate, gap distance between electrodes, and the number of discharges on product distribution and energy efficiency were studied. Dependent on conditions, energy efficiencies in the order of 80%, methane conversion up to 75%, and carbon selectivity toward C2+ products up to 90% can be achieved for these processes. The performance of this plasma-chemical microreaction system uses around two-thirds of the energy of that for the current commercial ethylene production process and is thus proposed as a promising alternative for industrial applications including valorization of stranded methane sources.